Technical Field
This relates generally to electronic devices, and more particularly, to electronic devices with a display.
Description of the Related Art
Electronic devices often include displays. For example, cellular telephones and portable computers include displays for presenting information to a user. Components for the electronic device, including but not limited to a display, may be mounted in the housing made of plastic or metal.
An assembled display may include a display panel and a number of components for providing a variety of functionalities. For instance, one or more display driving circuits for controlling the display panel may be included in a display assembly. Examples of the driving circuits include gate drivers, emission (source) drivers, power (VDD) routing, electrostatic discharge (ESD) circuits, multiplex (mux) circuits, data signal lines, cathode contacts, and other functional elements. There may be a number of peripheral circuits included in the display assembly for providing various kinds of extra functions, such as touch sense or fingerprint identification functionalities.
Some of the components may be disposed on the display panel itself, often in the areas peripheral to the display area, which is referred in the present disclosure as the non-display area and/or the inactive area. When such components are provided in the display panel, they populate a significant portion of the display panel. Large inactive area tends to make the display panel bulky, making it difficult to incorporate it into the housing of electronic devices. Large inactive area may also require a significant portion of the display panel to be covered by overly large masking (e.g., bezel, borders, covering material), leading to unappealing device aesthetics.
Size and weight are of the critical importance in designing modern electronic devices. Also, a high ratio of the active area size compared to that of inactive area, which is sometimes referred to as the screen to bezel ratio, is one of the most desired feature. There is a limit as to how much reduction in the size of the inactive area for higher screen-to-bezel ratio can be realized from mere use of a separate flexible printed circuit (FPC) for connecting components to the display panel. Space requirement for reliably attaching signal cables and to fan out wires along the edges of the display panel still needs to be disposed in the inactive area of the display panel.
It will be highly desirable to bend the base substrate where the active with the pixels and the inactive area are formed thereon. This would truly minimize the inactive area of the display panel that needs to be hidden under the masking or the device housing. Not only does the bending of the base substrate will minimize the inactive area size need to be hidden from view, but it will also open possibility to various new display device designs.
However, there are various new challenges that need to be solved in providing such flexible displays. The components formed directly on the base substrate along with the display pixels tend to have tremendously small dimension with unforgiving margin of errors. Further, these components needs to be formed on extremely thin sheet to provide flexibility, making those components extremely fragile to various mechanical and environmental stresses instigated during the manufacture and/or in the use of the displays.
Further complication arises from the fact that the components fabricated directly on the base substrate with the display pixels are often closely linked to the operation of those pixels. If care is not taken, the mechanical stresses from bending of the flexible display can negatively affect the reliability or even result in complete component failure. Even a micro-scale defect in the component thereof can have devastating effects on the performance and/or reliability of the display pixels amounting to scrap the entire display panel without an option to repair.
For instance, a few micrometer scale cracks in the electric wires can cause various abnormal display issues and may even pixels in several rows or sections of the display panel not to be activated at all. As such, there are various special parameters that must be taken in consideration when designing electrical wiring schemes to be fabricated directly on the flexible base substrate along with the display pixels.
Simply increasing the bending radius may make it difficult to garner any significant benefits in flexing the base substrate of the display panel. With extremely small bending radius, it is a daunting task to provide a flexible display which allows the base substrate to be bent or otherwise deformed without losing the functionality. It would therefore be desirable to provide a flexible display that can operate reliably even under the bending stresses from extreme bending radius.